Method and system for laying a pipeline from a reel barge

ABSTRACT

A method and system for laying an underwater pipeline from a barge-mounted reel which supports a coil of elasto-plastic pipe. The coil contains many layers, each formed by a plurality of variable-diameter convolutions. To make the effectiveness of the system substantially independent of the diameter of the convolution from which the pipe emerges, and to facilitate the threading through the system of the pipe span emerging from the reel, the curved emerging span is reverse-bent beyond its elastic range to a predetermined radius sufficient to prevent buckling the span. Subsequently, the reverse-bent pipe is passed through a straightener for imparting to the pipe a substantially rectilinear configuration.

nited States atent 1 Key et al.

[54] METHOD AND SYSTEM FDR LAYING A PIPELINE FROM A REEL BARGE [7 5] lnyentorsz Joe Wayne Key, Lari'y Rayner Russell, both of Houston, Tex.

Tex.

[58] Field 0i Search ..72/161, 160, 205,165,164, 72/166,183;6l/72.3;242/78.6, 128

[56] References Cited UNITED STATES PATENTS 3,260,092 7/1966 Greven..72/164 X 3,372,461 3/1968 Tesson ..29/429 3,237,438 3/1966 Tesson..72/16l 3,442,108 5/1969 Muller ..72/l64 2,346,990 4/1944 Oftedal etal.. ..72/161 3,422,653 1/1969 Wiig ..72/161 6/1956 Miller ..72/1663/1950 Todd ..72/163 Primary ExaminerMilton S. Mehr Attorney-Michael P.Breston [57] ABSTRACT A method and system for laying an underwaterpipeline from a barge-mounted reel which supports a coil ofelasto-plastic pipe. The coil contains many layers, each formed by aplurality of variable-diameter convolutions. To make the effectivenessof the system substantially independent of the diameter of theconvolution from which the pipe emerges, and to facilitate the threadingthrough the system of the pipe span emerging from the reel, the curvedemerging span is reverse-bent beyond its elastic range to apredetermined radius sufficient to prevent buckling the span.Subsequently, the reverse-bent pipe is passed through a straightener forimparting to the pipe a substantially rectilinear configuration.

12 Claims, 2 Drawing Figures 'PATENTEDJ AN23 1973 3,712,100

BY Michael PBreston A TTORNEV METHOD AND SYSTEM FOR LAYING A PIPELINEFROM A REEL BARGE CROSS-REFERENCE TO RELATED APPLICATIONS Particularpipe processing tools which are useful to this invention are describedand claimed in copending patent application Ser. No. 5,842, and now US.Pat. No. 3,680,3 42, assigned to the same assignee.

BACKGROUND OF THE INVENTION 1. Field of the Invention This inventiongenerally relates to the field of laying underwater pipelines from abarge-mounted reel.

2. Description of the Prior Art A known and presently used system forlaying smallto-medium diameter pipelines from a barge-mounted reel isdescribed in US. Pat. No. 3,237,438. In general, the known systeminvolves, on one hand, pre-bending and winding the pipe, and on theother hand, unwinding and reverse-bending the pipe.

The pre-bending and winding phase is accomplished by advancing straightsections of pipe toward a work station, joining the sections together asthey progress throughthe work station to form a continuous pipeline,plastically prebending a span of the pipeline leading to the reel,rotating the reel preferably abut a vertical axis, and winding thepipeline on the reel into a multi-layer coil.

The unwinding and processing phase involves reverse-bending the span ofpipe emerging from the reel and suitably guiding the straightened pipefrom the barge to the floor of the body of water.

In particular, for a better understanding of the known system, adetailed description will now be given using the reference characters ofthe drawings in said patent. The emerging span of pipe 13 from reel 11has its curvature removed by reverse-bending in a straightener 17 whichis provided with two pairs of end rolls 41, 43 and a center pair ofworking rolls 42. Between the centers of rolls 41 and 43 is defined ahorizontal path line. The amount of straightening or reverse-bending ofthe emerging pipespan is determined by the horizontal distance from thecenter of working rolls 42 transverse to the horizontal path line.Straightener 17 is mounted on a platform 18 and is supported forreciprocal vertical movement on vertical posts to allow the horizontalpath line to become in vertical alignment with each pipe convolution asit unwinds from reel 11.

In the operation of the above known system, one finds that the radius ofcurvature of the emerging pipe span from reel 11 varies from a minimumradius, corresponding to the innermost pipe layer, to a maximum radius,corresponding to the outermost pipe layer. Since the transversehorizontal distance from the working rolls 42 to the horizontal pathline is generally maintained constant, the amount of reverse-bending isalso constant, irrespective of the reduction in the diameter of theunwinding coil and, hence, irrespective of the curvature in thecurvilinear pipe span emerging from reel 11. Since the transversehorizontal distance is selected on the basis of the average curvature ofthe completely straightened by straightener l7. Incomplete straighteningmay leave some residual bending stresses and strains within the pipelineas it emerges from straightener 17. While the residual curvatures can beovercome, as by the proper application of axial or longitudinal tensionin the pipeline, they cannot be completely removed by such appliedtension.

To alleviate the residual stress problem, an operator, in carrying outthe known method, could continuously manually adjust the transversehorizontal distance between the working rolls 42 and the horizontal pathline by an amount which is correlated with the instantaneous diameter ofthe coil as it unwinds.

But, at the rate it is desired to lay the pipe, such a continuous manualadjustment would be a most difficultjob, even ifa skilled operator coulddetermine, by observation or from instrumentation, the optimum amount ofrequired adjustment.

It may be also contemplated to provide, for the working rolls 42,automatic adjusting and positioning means, but the cost, complexity andlack of reliability for continuous use of such automatic adjusting meansmake such a solution rather unattractive.

Another consideration in the practice of the above method stems from avariable angle of entry into the pipe straightener 17. Theabove-mentioned horizontal path line is selected so as to be tangent toa middle layer in the coil, that is, to approximately bisect the anglesustained by the diameter of the full coil from the entry point to thestraightener. Hence, the curved pipe span emerging from the outermostpipe layer on the coil will be at a maximum working angle of onepolarity relative to this tangent in a horizontal plane, and whenemerging from the innermost layer it will be at a maximum working angleof the opposite polarity. Consequently, if the pipes path line remainsstationary in a horizontal plane, this working angle will decrease asthe diameter of the unwinding coil becomes reduced. If the horizontalpath line were made movable transversely to follow the reduction in thecoils diameter, it would be necessary to mount the straightener both forreciprocal horizontal movement, as well as for reciprocal verticalmovement. A straightener so mounted would require a wide span in ahorizontal plane on the deck of the barge, as well as cumbersome supportstructures which are normally coupled to the barge for guiding the pipeonto the floor of the body of water.

For a better understanding of the problems which may be encountered withprior art systems, as well as of the advantages of the system of thepresent invention, a simplified review will be given of the bendingstressstrain relationship within a pipe made from an elastoplasticmetal.

In the elastic or straight-line range the stress is proportional to theresultingstrain. When the stress is released, the strain returns to itsoriginal balanced value or zero curvature. The limit of the elasticrange is reached when the strain no longer returns to its zerocurvature. This limit corresponds to the greatest stress the pi'pesmaterial can withstand without producing a residual deflection orcurvature.

Beyond the elastic range, that is in the plastic or flat-line range, theapplied bending stress exceeds the pipes elastic limit, and theproportional stress-strain relationship no longer holds. For a smallincrease in applied bending stress, there now is obtained asubstantially greater increase in resulting curvature. The boundarybetween the elastic range and the plastic range is commonly referred toas the yield point.

As one continues to bend the pipe past its yield point, the bendingstress or moment increases relatively slowly toward an ultimate value.The pipes curvature on the other hand increases to a critical curvatureat which buckling impends. Although most of the mathematical theories ofplasticity deal with ideal" plastic materials, most commerciallyavailable line pipe metals deviate somewhat from the ideal. It istherefore best to experimentally establish design parameters and tomeasure the critical moment required to bend the pipe to its criticalcurvature. The critical moment is a function of the pipes diameter, wallthickness and grade.

A material which is plastic becomes elastic when the applied stress isreduced in magnitude below the yield stress. Experimental curves showthat upon progressively reducing the applied moment from any point onthe flat plastic curve, there follows a descending elastic straight linesubstantially parallel to the original elastic line. The residualcurvature is that curvature which remains after the applied moment isreduced to zero. The progressive re-application of the moment to thepipe will follow an ascending elastic straight line from the residualcurvature. This ascending line initially is substantially parallel tothe original elastic line, and subsequently joins the plastic line afterthe yield point of the pipes material is reached.

SUMMARY OF THE INVENTION It is an object of the present invention toovercome the above-mentioned prior art shortcomings and to provide a newand improved method and system for laying pipelines from reels. Thesystem requires a minimum of adjustments, hand labor, complexinstrumentation, deck space and pipe support structures.

These and other readily apparent objects are accomplished in accordancewith a broad aspect of this invention by: reverse bending the pipe spanemerging from the reel preferably to a constant radius of curvaturesufficient to prevent buckling, and subsequently straightening thereverse-bent pipe. In accordance with a specific aspect of thisinvention, said constant radius is made substantially equal to orgreater than the minimum radius required to prevent buckling of thegreatest diameter pipe anticipated to be wound on and unwound from thereel.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a top view illustrating apreferred embodiment of the invention; and

FIG. 2 is a side elevation view of the embodiment shown in FIG. 1. I

Referring now to the drawings, wherein the showings are for the purposeof illustrating the preferred method and system of the invention only,and not for the purpose of limiting same, a suitable barge supports areel 12 for rotation about a vertical axis 11. Reel 12 winds and unwindsa continuous length of pipeline 16. While reel 12 is shown mounted forrotation about a vertical axis, it is appreciated that it could beequally mounted for rotation about a horizontal axis, but withappropriate changes in the positions of the pipe processing elements.

Pipeline 16 is preferably made of an elasto-plastic steel material of asuitable grade and may have a relatively large diameter, say between 4to 12 inches, and even higher. For example, a standard X-Grade pipecould be a 12 inch line pipe, Schedule 20 through 80, API 5L, Grade B,seamless, or a 6 inch line pipe, Schedule 20 through 180. For underwaterapplications, pipeline 16 is ordinarily covered with a suitableprotective coating, although such coating is not essential.

It has been found, contrary to what might be expected that neither thecoating nor the pipeline becomes damaged by the consecutive bending andreverse-bending operations contemplated by the method of this invention.

Reel 12 can be rotated by any known suitable means. During the windingand unwinding operations, a span of pipeline 16 passes through a system14 which includes a combined bending-and-level wind apparatus 18 and atension-control mechanism 42. System 14 is mounted on a frame 24 whichis reciprocable vertically on a plurality of posts 26.

To facilitate the winding of pipeline 16, the core 28 of reel 12 is madefrusto-conical. A preferred construction of reel 12 and the manner ofits operation is fully described in copending application Ser. No.5,840, and now US Pat. No. 3,630,461, assigned to the same assignee.Pipeline 16 is wound into a multi-layer coil 30. Each pipe layerincludes several pipe convolutions 32. The radius of curvature of thepipes span 34 when emerging from the innermost layer 36 has the smallestradius of curvature and when emerging from the outermost layer 38 hasthe largest radius of curvature. Also, within each layer, the radius ofcurvature decreases as the pipe span 34 emerges from the bottomconvolution to the top convolution.

As can be seen from FIG. 1, when the pipe span 34 emerges from theoutermost layer 38 it is at a relatively small angle A from a transversehorizontal line B, and when it issues from the innermost layer 36 it isat a relatively large angle C from line B. Thus, the emerging pipe span34 has a variable angle of entry into the bending apparatus 18. Theinstantaneous magnitude of the angle depends on the diameter of theparticular convolution 32 from which pipe span 34 emerges.

The exact configuration of the emerging pipe span 34 between reel 12 andapparatus 18 depends on the physical characteristics of pipeline l6 andthe stresses 1 within the pipe. An inflection point 40 occurs within theemerging pipe span 34 between reel 12 and bending apparatus 18. Beforereaching point 40 from reel 12, the span 34 has a positive curvature,and following point 40 a negative curvature. The terms positive andnegative have been arbitrarily selected only for ease of description. Asherein employed, a positive curvature is a curvature the radius of whichhas a center below the path of span 34 (as shown in FIG. 1) and,conversely, a negative curvature has its center above the path of span34.

In mathematical terms the radius of curvature of a segment of a curve isthe reciprocal of the curvature K, that is l/K, in which K is equal tothe change in the direction of the curve per unit length of are. Theradius of curvature of a straight line is infinite and that of a circleis the radius used to generate the circular curve. The radius ofcurvature ofa complex curve is a variable which depends upon thecurvatures of the infinitesimally-long circular arcs located at adjacentpoints on the curve.

The inflection point 40 is therefore a point where the pipes curvaturechanges signs. The bending apparatus 18 is adapted to receive theemerging span 34 at a variable angle of entry and at a variablecurvature, and to automatically bend the pipe so as to render it substantially free of residual stresses and strains for subsequent use duringthe pipe-laying operation.

To better appreciate the present invention, each of the basic componentsof the system will be discussed in some detail; however, it isunderstood that various structural changes may be made in some or all ofthese components without departing from the scope of the presentinvention. The detail structure of the components forming the system isfully described in said U.S. Pat. No. 3,680,342. Hence, only a briefdescription thereof, sufficient to understand the present invention, isgiven herein.

The bender 18 is designed to compound-bend the merging pipe span 34. Forsimplicity of construction, a three-roll compound bender is employedwhich in cludes three tools 50, 52 and 54 positioned at spaced locationsrelative to each other and to reel 12. Pipe span 34 is extended throughthese tools, as shown. The peripheral face of each tool has a movablechain hear ing resilient blocks that are arcuately shaped to receive andclosely engage against one side of the pipe span. The radius ofcurvature of each chain in each of tools 52 and 54 is adjustable from aninfinite radius of curvature (flat) to a minimum radius sufficient toprevent pipe buckling, thereby allowing the variation of the amount ofcurvature imparted to or removed from the pipe span 34. The bending tool50, on the other hand, applies a transverse force in a horizontal planewhich is operable to impart to pipe span 34 a negative curvaturecorresponding to the radius of curvature of its peripheral face inengagement with the pipe span 34.

During the winding operation, pipeline 16 is plastically bent byyielding the metal of the pipe beyond its elastic range to set therein apositive curvature in each convolution 32. During the unwindingoperation, bending tool 50 stresses the emerging span 34 as it passesthrough bender 18 to thereby yield the pipes material and to plasticallybend span 34 beyond its elastic range to a negative curvature having aconstant radius suffi cient to prevent buckling the pipeline.

Accordingly, the emerging pipe span 34 exiting from bending tool 50 at atangent point 56 will have a constant negative plastic curvature,irrespective of the diameter of the unwinding coil 30. Hence, thepipeline, when entering bender apparatus 18, has a non-uniformcurvature, and, when exiting from tool 50, has a uniform curvature,irrespective of the diameter of the unwinding coil. Therefore, bendingtool 50 may be considered as a stress uniformizer and as a curvatureuniformizer.

Pipe span 34, as it exits from bending tool 50, is curvilinear. It isthe function of the other remaining tools to transform this curvilinearprofile of pipeline 16 into a rectilinear profile. For this purpose thecenter bending tool 52 applies a moment to pipe span 34, which momentimparts to it a positive curvature. This is accomplished by plasticallybending pipe span 34 beyond its elastic range to a particular positivecurvature.

Thereafter, as the pipe moves past device 52 and toward device 54, theinduced bending moment in span 34 is unloaded along a linearly elasticpath, resulting in a pipe profile which is substantially rectilinear andwhich is characteristic of a state of substantially zero net moment inpipeline 16. I

The tension-control mechanism 42 maintains the emerging pipe span 34under tension while it is being compound-bent by bender apparatus 18.The tensioner 42 in the preferred embodiment includes two opposed trackchains 46, 48, at least one of which is powered for rotation. Each chainalso bears resilient blocks having a groove therein so shaped as toreceive and snugly engage one side portion of the pipe. The chains movein the direction indicated by the arrows 49 during the unwindingoperation, and they also assist in pulling the pipe off reel 12.

Tool 54 defines with the center line of the tensioner 42 a horizontalpath line 60, and the amount of working or bending by tool 52 isdetermined by the adjustable, transverse, horizontal distance from theperiphery of tool 52 to this horizontal path line, as will beappreciated by those skilled in the art. It will also be apparent thatthe pipe span 34 between tools 50 and 52 sustains a sign reversal in itscurvature and has a second inflection point 62 near bending tool 52.

The system of this invention is effective for pipes of differentdiameters. While, in operation, relative horizontal position adjustmentsof tools 50 and 54 are not required, it is appreciated that should suchadjustments be required, they could be easily provided for either tool,or in a manner as to move the tools through a single control.

As stated, the tensioner 42 is suitably supplied with motive power. Onthe other hand, the tensioner may be eliminated, for example, bysecuring one end of the pipe to the seabed and pulling the barge by tugsand the like along the lay line, so that the pipe would be pulled offreel 12 by the motion of the barge.

Moreover, though only one reel is shown mounted on barge 10, it will beevident that more than one reel could be employed. In fact, such reelscould be stacked one above the other and used to pay out a plurality ofpipelines simultaneously or sequentially.

Each of tools 50, 52 and 54 may be a wheel or a portion of a wheel. Theperipheral face of each of tools 52 and 54 may vary from a straight lineto a relatively short radius of curvature. To allow for the processingof pipes of different diameters, the constant radius of curvature forthe bending tool 50 is selected so as to prevent buckling of the largestdiameter pipe expected to be processed by bending apparatus 18 and so asto prevent ovaling" of the pipe. The curvature of the peripheral face ofthe center or working tool 52 is adjustable to accommodate pipes ofvarying diameters through the bender 18.

One or more guide structures or stanchions, generally designated as 70,carry supports 71 for guiding the rectilinear pipeline 16 which exitsfrom the tensioner 42 along a vertically inclined, pipe-processing path72 to facilitate the pipes entry into thebody of water.

Any suitable means 74, which may be cam operated and controlled, may beemployed to reciprocate vertically the supports 71 as well as theplatform 24 on which are mounted tools 50, 52, 54, and tensioner 42. Thereciprocation is synchronized with the rotation of reel 12.

The preferred system 14 of the present invention allows the unwinding ofa pipeline from a reel at a relatively high rate of speed without theneed to continuously manually or otherwise adjust the bending tools ofconventional benders. The system accepts pipes of varying diameters andis especially beneficially employed with relatively-large diameterpipes, up to 12 inches and higher. The emerging curvilinear pipe fromthe reel is rendered substantially rectilinear without unbalancedresidual moments remaining therein. Also, the system is substantiallyindependent of the prior loading history of pipeline 16.

While the description has been so far particularly directed to apreferred apparatus, it will be appreciated that other known tools canbe employed for carrying out the novel steps of this invention. Forexample, a three-roll bender of known design, such as is disclosed inUS. Pat. 3,237,438, can be used after the pipe span 34 exits from thebending tool 50.

While the operation of the disclosed apparatus was particularly directedto the unwinding phase, it will be appreciated that the winding phasecan be equally accomplished with the apparatus of this invention. Inaddition, the compound bending of the pipe, during the winding andunwinding operations, is also effected by vertical movement of theentire frame 24. This vertical movement is effected by the power means74. Power means 74 can be hydraulically-operated cylinders which couldalso be useful in moving the various tools 50, 52, 54 and 42 relative toeach other in a conventional manner.

During the winding operation, sections of pipe in standard lengths aremoved through a welding station and joined together to form thepipeline. The pipeline is then prebent and wound onto the reel 12 duringthis joining operation. The prebending is to a curvature depending onthe diameter of the reel employed and on the diameter of the pipe.

It will be therefore obvious that many other modifications may be madein the apparatus particularly disclosed herein. The invention istherefore not to be considered limited to the preferred embodimentsshown in the drawings, but rather only by the scope of the appendedclaims.

What is claimed is:

1. An apparatus for straightening a long line of elasto-plastic metalpipe wound on a reel including:

means for unwinding the pipeline from the reel,

means for reverse-bending said pipeline beyond its elastic range to asubstantially uniform curvilinear configuration as it is being unwound,and

means for again reverse-bending said pipeline beyond its elastic rangeto a substantially rectilinear configuration after said pipelinesubsequently reverse-bending said pipeline beyond its elastic range to arectilinear configuration after said pipeline acquires said curvilinearconfiguration, and

maintaining said pipeline under tension during the unwinding of saidpipeline.

3. The method of claim 2 and further including:

maintaining said pipe under tension during said unwinding step.

4. An apparatus for handling a relatively-inflexible metal pipeline,said apparatus including:

a reel rotatable about its axis;

means for rotating said reel in opposite directions for respectivelywinding pipe thereon and unwinding pipe therefrom;

combined bending-and-level-wind means mounted adjacent said reel, saidmeans comprising:

a first, a second and third surfaces,

each surface being mounted for rotation about an axis extendingsubstantially parallel to the axis of said reel,

each pair of surfaces being at opposite sides of the line of travel ofsaid pipeline,

said surfaces being curved and being operable to engagelongitudinally-spaced segments of a portion of said pipeline,

means operatively coupled with said surfaces for maintaining andselectively moving said portion of said pipeline against said surfaces,thereby allowing said surfaces to exert on the engaged portion of saidpipeline longitudinally-spaced, operating forces, while said pipeline isbeing wound on and unwound from said reel, and

the radius of said first surface and the radius of said second surfacebeing sufficiently great to bend and reverse bend said pipeline whilesaid pipeline is being wound on and unwound from said reel beyond itselastic range.

5. The apparatus of claim 4 and further including:

means for maintaining said pipe under tension while said pipeline beingwound on and unwound from said reel.

6. The apparatus of claim 5 and further including:

means for movably supporting said pipeline at spaced positions in avertical plane, and

said positions being adjustable to allow said pipeline to assume aprogressively decreasing vertical elevation and to enter into a body ofwater along a downwardly'direeted path. 7. An apparatus for uncoiling arelatively-inflexible metal pipeline wound on the hub of a reelrotatably mounted on a support, said apparatus comprising:

means for unwinding the pipeline from the hub of the reel whilemaintaining the pipeline under tension;

means for reverse-bending the pipeline beyond its elastic range, as itis being unwound from the reel, to a constant bending radius, therebyproviding the pipeline with a substantially-uniform, residual stressdistribution pattern at any cross section along its longitudinal axis;and

straightener means for straightening the thusly bent pipeline.

8. A method of laying a pipeline made of metal from the deck of afloatable platform onto the bed of a body of water, comprising the stepsof:

unwinding the pipeline from the hub of a reel which is rotatably mountedon said deck,

reverse-bending the pipeline beyond its elastic range, as it unwindsfrom the reel, to a constant bending radius,

straightening the thus bent pipeline and maintaining it under tensionwhile it is being straightened, and

moving the straightened pipeline into the body of water overlying thedesired location of the pipeline on said bed.

9. The method according to claim 8, wherein the pipeline, after it isreverse bent to said constant bending radius, acquires a uniform,residual stress distribution pattern at any cross-section along itslongitudinal axis.

10. An apparatus for laying a pipeline made of metal from the deck of afloatable platform onto the bed of a body of water, said pipeline beingwound into a coil around the hub of a reel which is rotatably mounted onsaid deck, said apparatus comprising:

means for unwinding said pipeline from said reel,

a bending member for reverse-bending the pipeline beyond its elasticrange to a constant bending radius as the pipeline unwinds from saidreel,

a straightening member for straightening the pipeline after it has beenbent by the bending member, and

means for moving the unwound portion of the pipeline into the body ofwater overlying the desired location of said pipeline on said bed.

1 1. The apparatus of claim 10, and

a guiding member, disposed relative o the longitudinal axis of saidpipeline on the opposite side of said straightening member and on thesame side as said bending member, for effectively positioning andmaintaining the moving pipeline on said straightening member.

12. The apparatus of claim 11, and

a tensioner having at least two tensioning members oppositely disposedrelative to the longitudinal axis of said moving pipeline to maintainsaid pipeline under tension while it is being straightened by saidstraightening member.

1. An apparatus for straightening a long line Of elasto-plastic metalpipe wound on a reel including: means for unwinding the pipeline fromthe reel, means for reverse-bending said pipeline beyond its elasticrange to a substantially uniform curvilinear configuration as it isbeing unwound, and means for again reverse-bending said pipeline beyondits elastic range to a substantially rectilinear configuration aftersaid pipeline acquires said curvilinear configuration.
 2. A method forstraightening a long line of elasto-plastic metal pipe wond on a reelincluding the steps of: unwinding the pipeline from the reel,reverse-bending said pipeline beyond its elastic range to a curvilinearconfiguration as it is being unwound, subsequently reverse-bending saidpipeline beyond its elastic range to a rectilinear configuration aftersaid pipeline acquires said curvilinear configuration, and maintainingsaid pipeline under tension during the unwinding of said pipeline. 3.The method of claim 2 and further including: maintaining said pipe undertension during said unwinding step.
 4. An apparatus for handling arelatively-inflexible metal pipeline, said apparatus including: a reelrotatable about its axis; means for rotating said reel in oppositedirections for respectively winding pipe thereon and unwinding pipetherefrom; combined bending-and-level-wind means mounted adjacent saidreel, said means comprising: a first, a second and third surfaces, eachsurface being mounted for rotation about an axis extending substantiallyparallel to the axis of said reel, each pair of surfaces being atopposite sides of the line of travel of said pipeline, said surfacesbeing curved and being operable to engage longitudinally-spaced segmentsof a portion of said pipeline, means operatively coupled with saidsurfaces for maintaining and selectively moving said portion of saidpipeline against said surfaces, thereby allowing said surfaces to exerton the engaged portion of said pipeline longitudinally-spaced, operatingforces, while said pipeline is being wound on and unwound from saidreel, and the radius of said first surface and the radius of said secondsurface being sufficiently great to bend and reverse bend said pipelinewhile said pipeline is being wound on and unwound from said reel beyondits elastic range.
 5. The apparatus of claim 4 and further including:means for maintaining said pipe under tension while said pipeline beingwound on and unwound from said reel.
 6. The apparatus of claim 5 andfurther including: means for movably supporting said pipeline at spacedpositions in a vertical plane, and said positions being adjustable toallow said pipeline to assume a progressively decreasing verticalelevation and to enter into a body of water along a downwardly-directedpath.
 7. An apparatus for uncoiling a relatively-inflexible metalpipeline wound on the hub of a reel rotatably mounted on a support, saidapparatus comprising: means for unwinding the pipeline from the hub ofthe reel while maintaining the pipeline under tension; means forreverse-bending the pipeline beyond its elastic range, as it is beingunwound from the reel, to a constant bending radius, thereby providingthe pipeline with a substantially-uniform, residual stress distributionpattern at any cross section along its longitudinal axis; andstraightener means for straightening the thusly bent pipeline.
 8. Amethod of laying a pipeline made of metal from the deck of a floatableplatform onto the bed of a body of water, comprising the steps of:unwinding the pipeline from the hub of a reel which is rotatably mountedon said deck, reverse-bending the pipeline beyond its elastic range, asit unwinds from the reel, to a constant bending radius, straighteningthe thus bent pipeline and maintaining it under tension while it isbeing straightened, and moving the straightened pipeline into the bodyof water overlying the deSired location of the pipeline on said bed. 9.The method according to claim 8, wherein the pipeline, after it isreverse bent to said constant bending radius, acquires a uniform,residual stress distribution pattern at any cross-section along itslongitudinal axis.
 10. An apparatus for laying a pipeline made of metalfrom the deck of a floatable platform onto the bed of a body of water,said pipeline being wound into a coil around the hub of a reel which isrotatably mounted on said deck, said apparatus comprising: means forunwinding said pipeline from said reel, a bending member forreverse-bending the pipeline beyond its elastic range to a constantbending radius as the pipeline unwinds from said reel, a straighteningmember for straightening the pipeline after it has been bent by thebending member, and means for moving the unwound portion of the pipelineinto the body of water overlying the desired location of said pipelineon said bed.
 11. The apparatus of claim 10, and a guiding member,disposed relative o the longitudinal axis of said pipeline on theopposite side of said straightening member and on the same side as saidbending member, for effectively positioning and maintaining the movingpipeline on said straightening member.
 12. The apparatus of claim 11,and a tensioner having at least two tensioning members oppositelydisposed relative to the longitudinal axis of said moving pipeline tomaintain said pipeline under tension while it is being straightened bysaid straightening member.